Cytotoxicity-related Gene Expression and Chromatin Accessibility Define a Subset of CD4+ T Cells that Mark Progression to Type 1 Diabetes

Type 1 diabetes in children is heralded by a preclinical phase defined by circulating autoantibodies to pancreatic islet antigens. How islet autoimmunity is initiated and then progresses to clinical diabetes remains poorly understood. Only one study has reported gene expression in specific immune cells of at-risk children, associated with progression to islet autoimmunity. We analysed gene expression by RNAseq in CD4⁺ and CD8⁺ T cells, NK cells and B cells, and chromatin accessibility by ATACseq in CD4⁺ T cells, in five genetically at-risk children with islet autoantibodies who progressed to diabetes over a median of 3 years (‘Progressors’) compared to five children matched for sex, age and HLA-DR who had not progressed (‘Non-progressors). In Progressors, differentially expressed genes (DEGs) were largely confined to CD4⁺ T cells and enriched for cytotoxicity-related genes/pathways. Several top-ranked DEGs were validated in a semi-independent cohort of 13 Progressors and 11 Non-progressors. Flow cytometry confirmed progression was associated with expansion of CD4⁺ cells with a cytotoxic phenotype. By ATAC-seq, progression was associated with reconfiguration of regulatory chromatin regions in CD4⁺ cells, some linked to differentially expressed cytotoxicity-related genes. Our findings suggest that cytotoxic CD4⁺ T cells play a role in promoting progression to type 1 diabetes.